600 
Vol. XXIX, No. 12 
Journal oj Agricultural Research 
cent milk. A price differential greater 
than that indicated is favorable to the 
production of high-testing milk; while 
a smaller differential is favorable to 
the production of low-testing milk. 
Obviously, the price differential 
should be considered relative to the 
price of milk. Figure 2 shows in the 
form of a frequency distribution curve 
the differentials for 101 cities taken 
from the August, 1923, market report 
above referred to. 
The differential is expressed as a per 
cent of the price 8 of 3.5 per cent milk, 
be more simply accomplished by ad¬ 
justing the price according to one of 
the following formulae, in which t 
stands for fat percentage and P 3 . 0 , the 
price of 3.0 per cent milk; P 3 . 5 , the 
price of 3.5 per cent milk; etc.: 
0.17668 P 30 (2.66+0 
.16234 P 35 (2.66+0 
.15015 P 4 'o (2.66+0 
.13055 P 50 (2.66 + 0 or, gener¬ 
alized, 
(reps) (P6) (2 - 66+0 
O .2 .4 .6 .6 AO t.2 t.4 1.6 AS 2.0 2.2 2.4 2.6 2JB 3.0 3.2 3.4 
Allowance for OJ%m Test-Expressed as a Per Centof the Prke per Cwr. of 3.5% M/lk 
Tig. 2.— Frequency distribution curve of 101 cities with respect to the differential in the price of milk 
according to the fat test of the milk. Data from August, 1923, “Milk Market Report.” The differ¬ 
ential is the price difference per hundredweight of milk for each difference of 0.1 in the per cent of fat in the 
milk. In order to make the data comparable it is expressed, in this figure, as a per cent of the price per 
hundredweight of 3.5 per cent milk. The broken line at 1.6 indicates the cost of production differential; 
that is, the difference in cost of production per hundredweight of milk for each difference of 0.1 in the per 
cent of fat in the milk (so far as the cost of milk production is affected by percentage fat content of the 
milk). The cost differential is expressed,likewise, as a per cent of the cost of production of 3.5 per cent 
milk. It is assumed that the cost of production is proportional to the feed cost 
and all cities are included where a 
definite price and differential are given. 
For the sake of comparison the cost of 
production differential is indicated in 
the figure, expressed likewise as a per 
cent of the cost of 3.5 per cent milk. 
Except for the two classes, 0 and 2.8, 
there appears to be a tendency toward 
a normal distribution curve centering 
about the cost of production as a mean. 
The class at 0 represents those cities 
paying a flat rate. The class at 2.8 
represents those cities paying, practi¬ 
cally, on a straight fat basis (a dif- 
ferntial of 2.857 per cent of the price 
of 3.5 per cent milk is a straight fat 
basis). 
An exact adjustment of price in pro¬ 
portion to cost is rather cumbersome 
by the system of a certain allowance 
per 0.1 per cent in the fat test. It may 
To illustrate the working of the above 
scheme, we may take the Chicago 
market for August, 1923, $3.20 per 
hundredweight for 3.5 per cent milk. 
The price for milks of other test, to 
bear the same ratio to cost of produc¬ 
tion, would be $0.16234 X 3.20 (2.66+ 
t) and $0.52 (2.66 + 0 would be the 
general expression for the price of 
milk for that month. Thus, 3.21 per 
cent milk would be $0.52 (2.66 + 3.21) 
= $3.05; 4.14 per cent milk would be 
$0.52 (2.66+4.14) =$3.54; etc. The 
prices actually paid were $3.08 and 
$3.46, respectively. 
SUMMARY 
The nutrients required for lactation 
per pound of milk, Nl, may be ex¬ 
pressed as a function of the fat per- 
8 This price is f. 0 . b. city. It would be better for this comparison to use country bjiying prices and 
weighted average for the year. The data for such a comparison are not available to the writer. 
